The present invention relates to a mask pattern correction method useful for correcting a pattern edge position in an optical proximity effect, and a recording medium which records the mask pattern correction program.
In recent years, the semiconductor manufacturing techniques have extremely progressed, and semiconductor devices having a minimum processible size of 0.25 .mu.m have been manufactured in these days. This fine downsizing of devices is realized by rapid progress of a fine pattern forming technique called an optical lithography technique. The optical lithography means a series of steps of: forming a mask from a design pattern of an LSI; irradiating light on the mask to expose a resist coated on the wafer in accordance with a pattern drawn on the mask by a projection optical system; and developing the resist based on the dose distribution thereby to form a resist pattern on the wafer. By etching lower layers with use of the resist pattern formed through the optical lithography steps, as a mask, an LSI pattern is formed on the wafer.
In a generation in which the pattern size was sufficiently large compared with the resolution limit of a projection optical system, the plan shape of the LSI pattern desired to be formed on the wafer was directly drawn as a design pattern. Further, a mask pattern as same as the design pattern was prepared. The mask pattern thus obtained was transferred onto a wafer by a projection optical system. In this manner, a pattern substantially similar to the design pattern was formed on the wafer.
However, as the patterns have come to become smaller, an optical proximity effect has come to appear clearly. Due to this optical proximity effect, the pattern formed on a wafer with use of a mask prepared in compliance with a design pattern differs from the design pattern, accompanying remarkable bad influences.
For example, in case of a line/space (L/S) pattern, the finished line widths in an isolated pattern and a dense pattern differ from each other. Similarly, in case of a two-dimensional pattern for a contact hole or the like, the finished plan shape of the pattern differs depending on the difference in the degree of pattern density or pitch. Therefore, the dose amounts used for finishing the isolated pattern and dense pattern in compliance with desired dimensions vary for every pattern. As a result, it is impossible to attain an exposure margin necessary for the lithography steps.
Hence, there has been a proposal for a method for moving pattern edge positions such that the finished plan shape exposed at a certain predetermined dose amount does not depend on the density or pitch of the pattern but is finished within certain predetermined dimensions. This is called an optical proximity effect correction, and movement amounts of pattern edge positions are optimized in the following procedures (1) to (3), in many cases.
(1) A dimensional difference .DELTA.x.sub.i1 between an edge position of a desired pattern, and an edge position of a finished plan shape, which is obtained by subjecting the mask pattern to an image intensity calculation, is calculated. In this case, i denotes an appended character corresponding to the edge, and the numeral following the character figure indicates the number of repetitive calculations.
(2) As for the dimensional difference .DELTA..sub.xi1 at each edge position, each edge position of the mask pattern indicated in (1) is moved by the length .DELTA.C=.DELTA.x.sub.i1 /M regulated by a constant M determined to be uniform for each edge, to prepare a corrected mask pattern.
(3) The calculations indicated in (1) and (2) are repeated until a dimensional difference .DELTA.x.sub.in between the edge position of the finished plan shape of the corrected mask pattern prepared in (2) and an edge position of a desired pattern becomes to be equal to a predetermined allowable value or less.
However, the constant M is a value which varies for each edge in complicated device pattern. Therefore, if a constant M is used uniformly for each edge, a repetitive calculation need to be carried out for a large number of times, so a long time is required. If the above-mentioned value of M and a value of M which is actually obtained by an edge greatly differs from each other, the dimensional difference .DELTA.xin obtained by calculations repeated for n times oscillates between + and - directions, so the calculations cannot be converged. Therefore, the movement amount of the edge position cannot be optimized in several cases due to the pattern layout.
FIG. 1 shows the relationship between the number of times of correction calculations and the correction results where corrections were made in accordance with the conventional procedures described above. The lateral axis represents the number of times for which calculations were repeated, while the longitudinal axis represents the mask dimension. In case of a aerial image calculation, the mask dimension value oscillates for every time of correction calculation. When calculations were made in consideration of development process in addition to the aerial image calculation, the mask dimension value is diverged. Thus, in neither the aerial image calculation nor the aerial image calculation considering development, the mask dimension value was converged.